Superjunction semiconductor device

ABSTRACT

In accordance with an embodiment of the invention, a superjunction semiconductor device includes an active region and a termination region surrounding the active region. A central vertical axis of a boundary column of a second conductivity type material defines the boundary between the active region and the termination region. The active and termination regions include columns of first and second conductivity type material alternately arranged along a horizontal direction in a semiconductor region having top and bottom surfaces. At least one of the columns of the first conductivity type material in the termination region has a different width than a width of the columns of the first conductivity type material in the active region.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority from Korean Patent Application No.2003-85765, filed Nov. 28, 2003, the disclosure of which is incorporatedherein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device, and moreparticularly to a superjunction semiconductor device having alternatingcolumns of p-type and n-type conductivity type material in the activeand termination regions.

Typically, in vertically conducting semiconductor devices the electrodesare disposed on two opposing planes. When the vertical semiconductordevice is turned on, drift current flows along the thickness (i.e.,vertical direction) of the semiconductor device. When the device isturned off, depletion regions extend vertically. To realize highbreakdown voltage for a vertical semiconductor device, a drift layerbetween the electrodes must be made from a high resistivity material andhave a relatively large thickness. However, the high resistivity and therelatively large thickness of the drift layer increase the on-resistanceof the device. A higher on-resistance adversely affects the performanceof the device by increasing the conduction loss and lowering theswitching speed. It is well known that on-resistance of a device rapidlyincreases in proportion to the 2.5^(th) power of a breakdown voltage (B.Jayant Baliga, Power Semiconductor Devices, 1996, PWS PublishingCompany, page 373).

One technique to overcome this problem has been to use a semiconductordevice with a particular junction structure. Such semiconductor deviceincludes alternating columns of opposite conductivity type materialformed in a drift layer in the active region of the device. Thealternating columns of opposite conductivity type material provide acurrent path when the device is turned on while it is depleted towithstand the reverse voltage when the device is turned off. Asemiconductor device with alternating columns of opposite conductivitytype material is hereinafter referred to as a “superjunctionsemiconductor device”.

For a superjunction semiconductor device, breakdown voltage of thedevice can be approximated by the product of the thickness of the driftlayer and the threshold electric field. In particular, if the chargequantities in the alternately arranged columns of high concentrationn-type and p-type material are in equilibrium with each other, thebreakdown voltage becomes independent of the resistivity of the driftlayer. For this reason, reducing the resistivity of the drift layer doesnot lead to a drop in breakdown voltage, thus realizing high breakdownvoltage and low on-resistance at the same time.

Despite the above advantages, the superjunction semiconductor device hasa drawback in that it is difficult to stably implement a terminationregion surrounding the active region. This is because the lowresistivity of the drift layer (due to high impurity concentration)causes the lateral electric field distribution in the transition regionfrom the active region to the termination region irregular, thusreducing the stability of the device. Furthermore, vertical electricfield distribution must meet predetermined conditions for obtaining highbreakdown voltage. If the vertical electric field distribution isignored, the breakdown voltage in the termination region may beundesirably lower than in the active region.

Thus, there is a need for a superjunction semiconductor device whereinboth the on-resistance and breakdown voltage are improved.

BRIEF SUMMARY OF THE INVENTION

In accordance with an aspect of the present invention, a superjunctionsemiconductor device has a termination structure which results in ahigher breakdown voltage in the termination region than that in theactive region.

In one embodiment of the invention, a superjunction semiconductor deviceincludes an active region and a termination region surrounding theactive region. A central vertical axis of a boundary column of a secondconductivity type material defines the boundary between the activeregion and the termination region. The active region and the terminationregion include columns of first conductivity type material and columnsof second conductivity type material alternately arranged on both sidesof the boundary column. A difference between a first conductivity typecharge quantity within a first column of the first conductivity typematerial in the termination region adjoining the boundary column and asecond conductivity type charge quantity in one half of the boundarycolumn and one half of a second column of the second conductivity typematerial in the termination region adjoining the first column is lessthan the difference between a first conductivity type charge quantitywithin a third column of the first conductivity type material in theactive region adjoining the boundary column and a second conductivitytype charge quantity in one half of the boundary column and one half ofa fourth column of the second conductivity type material in the activeregion adjoining the third column.

In another embodiment of the invention, a superjunction semiconductordevice includes an active region and a termination region surroundingthe active region. A central vertical axis of a boundary column of asecond conductivity type material defines the boundary between theactive region and the termination region. The active and terminationregions include columns of first and second conductivity type materialalternately arranged along a horizontal direction in a semiconductorregion having top and bottom surfaces. A spacing between the centralvertical axis of the boundary column and a central vertical axis of afirst column of the second conductivity type material in the terminationregion located closest to the boundary column is less than the spacingbetween the central vertical axis of the boundary column and a centralvertical axis of a second column of the second conductivity typematerial in the active region located closest to the boundary column.

In yet another embodiment of the invention, a superjunctionsemiconductor device includes an active region and a termination regionsurrounding the active region. A central vertical axis of a boundarycolumn of a second conductivity type material defines the boundarybetween the active region and the termination region. The active andtermination regions include columns of first and second conductivitytype material alternately arranged along a horizontal direction in asemiconductor region having top and bottom surfaces. The spacing betweenthe central vertical axes of the boundary column and a first column ofthe second conductivity type material in the termination region placedclosest to the boundary column is equal to the spacing between thecentral vertical axes of the boundary column and a second column of thesecond conductivity type material in the active region placed closest tothe boundary column. The width of the first column is greater than thewidth of the second column.

In yet another embodiment of the invention, a superjunctionsemiconductor device includes an active region and a termination regionsurrounding the active region. A central vertical axis of a boundarycolumn of a second conductivity type material defines the boundarybetween the active region and the termination region. The active andtermination regions include columns of first and second conductivitytype material alternately arranged along a horizontal direction in asemiconductor region having top and bottom surfaces. The spacing betweenthe central vertical axes of adjacent columns of the second conductivitytype material in the termination region becomes progressively greater ina direction away from the active region along a horizontal direction. Atleast one of the columns of the first conductivity type material in thetermination region has a different width than a width of the columns ofthe first conductivity type material in the active region.

In yet another embodiment of the invention, a superjunctionsemiconductor device includes an active region and a termination regionsurrounding the active region. A central vertical axis of a boundarycolumn of a second conductivity type material defines the boundarybetween the active region and the termination region. The active andtermination regions include columns of first and second conductivitytype material alternately arranged along a horizontal direction in asemiconductor region having top and bottom surfaces. At least one of thecolumns of the first conductivity type material in the terminationregion has a different width than a width of the columns of the firstconductivity type material in the active region.

BRIEF DESCRIPTION OF THE DRAWINGS

The above features and advantages of the present invention will becomemore apparent by describing in detail exemplary embodiments thereof withreference to the attached drawings in which:

FIG. 1 is a cross-section view of a superjunction semiconductor deviceaccording to an embodiment of the present invention; and

FIG. 2 is a cross-section view of a superjunction semiconductor deviceaccording to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

This invention may, however, be embodied in many different forms andshould not be construed as being limited to the embodiments set forthherein.

Referring to FIG. 1, a superjunction semiconductor device 100 accordingto an embodiment of this invention includes an active region I and atermination region II. Although it is not shown in FIG. 1, terminationregion II surrounds an edge region I-1. In general, edge region I-1indicates the outermost region of active region I. In active region Iand termination region II, an n-type region 120 is formed on an n-typesemiconductor substrate 110 serving as the drain region. A drainelectrode 130 is formed on the rear surface of drain region 110.

Columns of n-type and p-type material are alternately arranged in thelateral direction on n-type region 120 in both active region I andtermination region II. Boundary column 300 of p-type material forms thetransition region between active region I and termination region II.That is, active region I and termination region II are formed on theleft and right sides of a central vertical axis of boundary column 300,respectively. The invention is not limited to the particular number oftimes the alternating p-type and n-type columns are repeated in FIG. 1.Thus, the alternating p-type and n-type columns may be repeated agreater or smaller number of times than that shown in FIG. 1 as dictatedby the design and performance goals. Also, only a portion of the activeregion of the device is shown in FIG. 1. As is well known in this art,the planar gate cell structure shown at the far left edge of activeregion I is repeated many times.

The bottom surfaces of the alternating columns of p-type and n-typematerial in active region I-1 and termination region II are separatedfrom drain region 110 by the intervening n-type region 120. In analternate embodiment, the bottom surfaces of the alternating columns ofp-type and n-type material are in contact with the top surface of drainregion 110 without the intervening n-type region 120. A first edgeregion a1 closest to termination region II, which is the outermostregion of active region I, includes one half of column 300, n-typecolumn 211, and one half of p-type column 221. The p-type chargequantity within p-type columns 300 and 221 in the first edge region a1is smaller than the n-type charge quantity within n-type column 211.This is because the sum of the widths of p-type columns 300 and 221 issmaller than the width of n-type column 211. The first edge region a1where p-type charge quantities are not in balance with n quantities doesnot have an optimal breakdown voltage level. This is also the case withan adjacent second edge region a2 because the first and second edgeregions a1 and a2 have the same structure.

As in active region I, n-type columns 411, 412, 413, 414, and 415 andp-type columns 421, 422, 423, and 424 in termination region II arealternately arranged starting from p-type column 300. The widths ofp-type columns 421, 422, 423, and 424 are the same as those of p-typecolumns 221, 222, and 223 in active region I. The largest potential inthe termination region II is applied to a first termination region t1closest to active region I. Thus, the breakdown characteristics oftermination region II is significantly impacted by the first terminationregion t1 closest to active region I. The first termination region t1includes one half of p-type boundary column 300, n-type column 411, andone half of p-type column 421.

Spacing T1 between the central vertical axes of p-type columns 300 and421 in the first termination region t1 is less than spacing A betweenthe central vertical axes of p-type regions 300 and 221 in the firstactive edge region a1. This means that the p-type charge quantity withinp-type columns 300 and 421 and the n-type charge quantity within n-typecolumn 411 in the first termination region t1 are better balancedagainst each other than in the first active edge region a1. That is, inthe first active region a1, the n-type charge quantity is larger thanthe p-type charge quantity. But, in termination region t1, while thep-type charge quantity remains the same as that in edge region a1, then-type charge quantity is lower than that in edge region a1 since thespacing T1 is less than the spacing A. This reduces the difference inquantity between the p-type and n-type charges termination region t1 sothat both charge quantities may substantially equal. As the differencebetween the p-type and n-type charge quantities decreases in this way,the first termination region t1 exhibits higher breakdown voltagecharacteristics compared to active region I.

A second termination region t2 adjacent to the first termination regiont1 includes one-half of p-type column 421, the entire n-type column 412,and one-half of p-type column 422. A third termination region t3adjacent to the second termination region t2 includes one-half of p-typecolumn 422, the entire n-type column 413, and one-half of p-type column423. A fourth termination region t4 adjoining the third terminationregion t3 includes one-half of p-type column 423, the entire n-typecolumn 414, and one-half of p-type column 424.

Spacing T2 between the central vertical axes of p-type column 421 and422 in the second termination region t2 is greater than spacing T1 inthe first termination region t1. In an alternate embodiment, spacing T2is equal to spacing T1. Spacing T3 between the central vertical axes ofp-type columns 422 and 423 in the third termination region t3 is greaterthan spacing T2. Spacing T4 between the central vertical axes of p-typecolumns 423 and 424 in the fourth termination region t4 is greater thanspacing T3. This makes it possible to transmit the electric field whichwas concentrated at the first active edge region a1 and transmitted tothe first termination region t1 toward the edge of termination region IIat slower speed, thus realizing uniform horizontal distribution ofelectric field across the entire termination region II.

Along the far left side of active region I, a planar gate cell structureis shown. Although not show, this cell structure is repeated apredetermined number of times in the active region. The planar gatestructure includes a lightly doped p-type well region 231 which is overand in contact with a top surface of p-type column 223. Two highly dopedn-type source regions 232 are formed in well region 231. A highly dopedp-type well contact region 233 is formed in well region 231 between thetwo source regions 232. A gate insulating layer 234 and an overlyinggate electrode 235 are formed on each side of well contact region 233.The gate insulating layer and its overlying gate electrode to the rightof well contact region 233 overlap the source region on the right sideof well region 233, extend over a channel region along the top surfaceof well region 231 between the right source region and n-type column213, and extend over the adjacent n-type column 213. The gate insulatinglayer and its overlying gate electrode to the left of well contactregion 233 have a similar structure. A source electrode 236 contacts thetwo source regions 232 and well contact region 233 therebetween. Gateelectrode 235 and source electrode 236 are electrically insulated fromeach other by an insulating layer 237.

The operation of superjunction semiconductor device 100 will now bedescribed. When the device is turned on upon applying the proper biasingto the gate, drain and source electrodes, an inversion layer is formedin the channel regions within well region 231. A current path fromsource regions 232 laterally through the channel region, and thenvertically through n-type columns 213, 214, n-type region 120, substrate110, and drain electrode 130 is formed. Current flow between sourceelectrode 236 and drain electrode 130 is thus established. When thedevice is turned off, no current flows between the source and gateterminals, and the diode formed by the drain and well regions is reversebiased. The reverse bias causes a depletion region to extend in both thep-type and the n-type columns. The p-type and n-type columns aredepleted rapidly since the depletion region extends in both directionsat the same time. This makes it possible reduce the on-resistance byincreasing the doping concentration in n-type columns 211, 212, 213, and214 without adversely impacting the breakdown characteristics.

FIG. 2 illustrates a cross-section view of a superjunction semiconductordevice 500 according to another embodiment of this invention. In FIG. 2,the same reference numerals as in FIG. 1 represent the same element, soa detailed description thereof will be omitted. Superjunctionsemiconductor device 500 is different from the embodiment in FIG. 1 inthat spacing T1′ between the central vertical axes of p-type columns 300and 621 in a first termination region t1′ is equal to spacing A betweenthe central vertical axes of p-type columns 300 and 221 of the firstactive edge region a1. Another difference is that the widths of p-typecolumns 621, 622, 623, an d624 in termination region II differs from thewidth of p-type boundary column 300 and those of p-type columns 221,222, and 223 in active region I.

Specifically, active region I in superjunction semiconductor device 500is the same as that in superjunction semiconductor device 100 in FIG. 1.However, spacing T1′ between the central vertical axes of p-type columns300 and 621 of the first termination region t1′ located closest toactive region I is equal to spacing A between the central vertical axesof p-type columns 300 and 221 of the first edge region a1. Furthermore,the widths of the p-type columns in termination region II are greaterthan the width of p-type boundary column 300 and the p-type columns inactive region I. Consequently, the width of p-type region 621 in thefirst termination region t1′ is greater than those in the active regionsuch that the p-type charge quantity in termination region t1′ increasesrelative to those in active region a1, while the n-type charge quantitydecreases in termination region t1′ relative to those in active regiona1. Thus, the difference between the p-type charge quantity and then-type charge quantity in the first termination region t1′ is less thanthat in active region a1. Breakdown characteristics are thus improved.

Further, in superjunction semiconductor device 500, spacing T2′ betweenthe central vertical axes of p-type columns 621 and 622 in a secondtermination region t2′ is greater than the spacing T1′ in the firsttermination region t1′. In one embodiment, spacing T2′ is equal tospacing T1′. Spacing T3′ between the central vertical axes of p-typecolumns 622 and 623 in a third termination region t3′ is greater thanspacing T2′ in the second termination region t2′. Spacing T4′ betweenthe central vertical axes of p-type regions 623 and 624 in a fourthtermination region t4′ is greater than the spacing T3′ in the thirdtermination region t3′. This makes it possible to transmit the electricfield, which was concentrated at the first edge region a1 of activeregion I and transmitted to the first termination region t1′, toward theedge of termination region II less rapidly, thus realizing a uniformhorizontal distribution of electric field across the entire terminationregion II.

As described above, a superjunction semiconductor device according tothis invention has a more balanced p-type and n-type charge quantitiesin the termination region near the active region than in the activeregion, thus allowing the termination region to have higher breakdownvoltage than the active region. Furthermore, this invention allowsstable distribution of electric field on the surface of the device bychanging the spacing between the p-type columns (or the n-type columns)in the termination region thereby improving the device reliability.

The cross-section views of the different embodiments may not be toscale, and as such are not intended to limit the possible variations inthe layout design of the corresponding structures. Also, the varioustransistors can be formed in stripe or cellular architectures.

Although a number of specific embodiments are shown and described above,embodiments of the invention are not limited thereto. Various changesand modifications will occur to those For example, it is understood thatthe doping polarities of the structures shown and described could bereversed (e.g., to obtain p-type or n-type transistors) and/or thedoping concentrations of the various elements could be altered withoutdeparting from the invention. As another example, although only a planargate structure is shown in FIGS. 1 and 2, implementation of theinvention with other transistor structures such as trenched-gatestructures would be obvious to one skilled in this art in view of thisdisclosure. Also, the invention may be implemented in other types ofMOS-gated FETs such as IGBT's. Further, the features of one or moreembodiments of the invention may be combined with one or more featuresof other embodiments of the invention without departing from the scopeof the invention. Therefore, the scope of the present invention shouldbe determined not with reference to the above description but should,instead, be determined with reference to the appended claims, along withtheir full scope of equivalents.

1. A superjunction semiconductor device having an active region and atermination region surrounding the active region, a central verticalaxis of a boundary column of a second conductivity type materialdefining the boundary between the active region and the terminationregion, wherein the active region and the termination region includecolumns of first conductivity type material and columns of secondconductivity type material alternately arranged on both sides of theboundary column in a semiconductor region having top and bottomsurfaces, wherein a difference between a first conductivity type chargequantity within a first column of the first conductivity type materialin the termination region adjoining the boundary column and a secondconductivity type charge quantity in one half of the boundary column andone half of a second column of the second conductivity type material inthe termination region adjoining the first column is less than thedifference between a first conductivity type charge quantity within athird column of the first conductivity type material in the activeregion adjoining the boundary column and a second conductivity typecharge quantity in one half of the boundary column and one half of afourth column of the second conductivity type material in the activeregion adjoining the third column.
 2. The superjunction semiconductordevice of claim 1 wherein the active region further comprises aplurality of planar-gate structures formed along the top surface of thesemiconductor region.
 3. A superjunction semiconductor device having anactive region and a termination region surrounding the active region, acentral vertical axis of a boundary column of a second conductivity typematerial defining the boundary between the active region and thetermination region, the active and termination regions including columnsof first and second conductivity type material alternately arrangedalong a horizontal direction in a semiconductor region having top andbottom surfaces, wherein a spacing between the central vertical axis ofthe boundary column and a central vertical axis of a first column of thesecond conductivity type material in the termination region locatedclosest to the boundary column is less than the spacing between thecentral vertical axis of the boundary column and a central vertical axisof a second column of the second conductivity type material in theactive region located closest to the boundary column.
 4. Thesuperjunction semiconductor device of claim 3, wherein the width of athird column of the first conductivity type material in the activeregion is greater than the sum of one-half the width of a fourth columnof the second conductivity type material adjoining one side of the thirdcolumn and one-half the width of a fifth column of the secondconductivity type material adjoining the opposite side of the thirdcolumn.
 5. The superjunction semiconductor device of claim 3, whereinthe spacing between the central vertical axes of adjacent columns of thesecond conductivity type material in the termination region varies alonga horizontal direction.
 6. The superjunction semiconductor device ofclaim 3, wherein the spacing between the central vertical axes ofadjacent ones of at least three columns of the second conductivity typematerial in the termination region becomes progressively greater in adirection away from the active region.
 7. The superjunctionsemiconductor device of claim 3, wherein the first conductivity type isn-type, and the second conductivity type is p-type.
 8. The superjunctionsemiconductor device of claim 3 wherein the active region furthercomprises a plurality of planar-gate structures formed along the topsurface of the semiconductor region.
 9. A superjunction semiconductordevice having an active region and a termination region surrounding theactive region, a central vertical axis of a boundary column of a secondconductivity type material defining the boundary between the activeregion and the termination region, the active and termination regionsincluding columns of first and second conductivity type materialalternately arranged along a horizontal direction in a semiconductorregion having top and bottom surfaces, wherein the spacing between thecentral vertical axes of the boundary column and a first column of thesecond conductivity type material in the termination region placedclosest to the boundary column is equal to the spacing between thecentral vertical axes of the boundary column and a second column of thesecond conductivity type material in the active region placed closest tothe boundary column, and the width of the first column is greater thanthe width of the second column.
 10. The superjunction semiconductordevice of claim 9, wherein the width of a third column of the firstconductivity type material in the active region is greater than the sumof one-half the width of a fourth column of the second conductivity typematerial adjoining one side of the third column and one-half the widthof a fifth column of the second conductivity type material adjoining theopposite side of the third column.
 11. The superjunction semiconductordevice of claim 9, wherein the spacing between the central vertical axesof adjacent columns of the second conductivity type material in thetermination region varies along a horizontal direction.
 12. Thesuperjunction semiconductor device of claim 9, wherein the spacingbetween the central vertical axes of adjacent ones of at least threecolumns of the second conductivity type material in the terminationregion becomes progressively greater in a direction away from the activeregion.
 13. The superjunction semiconductor device of claim 9, whereinthe first conductivity type is n-type, and the second conductivity typeis p-type.
 14. The superjunction semiconductor device of claim 9 whereinthe active region further comprises a plurality of planar-gatestructures formed along the top surface of the semiconductor region. 15.A superjunction semiconductor device having an active region and atermination region surrounding the active region, a central verticalaxis of a boundary column of a second conductivity type materialdefining the boundary between the active region and the terminationregion, the active and termination regions including columns of firstand second conductivity type material alternately arranged along ahorizontal direction in a semiconductor region having top and bottomsurfaces, wherein the spacing between the central vertical axes ofadjacent columns of the second conductivity type material in thetermination region becomes progressively greater in a direction awayfrom the active region along a horizontal direction.
 16. Thesuperjunction semiconductor device of claim 15 wherein the active regionfurther comprises a plurality of planar-gate structures formed along thetop surface of the semiconductor region.
 17. A superjunctionsemiconductor device having an active region and a termination regionsurrounding the active region, a central vertical axis of a boundarycolumn of a second conductivity type material defining the boundarybetween the active region and the termination region, the active andtermination regions including columns of first and second conductivitytype material alternately arranged in a semiconductor region, wherein atleast one of the columns of the first conductivity type material in thetermination region has a different width than a width of the columns ofthe first conductivity type material in the active region.
 18. Asuperjunction semiconductor device having an active region and atermination region surrounding the active region, a central verticalaxis of a boundary column of a second conductivity type materialdefining the boundary between the active region and the terminationregion, the active and termination regions including columns of firstand second conductivity type material alternately arranged in asemiconductor region, wherein at least one of the columns of the secondconductivity type material in the termination region has a differentwidth than a width of the columns of the second conductivity typematerial in the active region.